Pulse multiplex system



Sept 30; 1947 E.'| AB1N ETAL 2,428,118

PULSE MULTIPLEX SYSTEM Filed April 7, 1944 7 vsheets-sham 1 @y M24 ilf M a 1 1 1 1 1 l, l l l 1|' a 5 J a a C j Il 'Il j l INVENToRsv ATToH/m Sept. 30,1947. E. L ABIN ETAL 2,428,118

PULSE MULTIPLEX. SYSTEM Filed April Y, l1944v 7 Sheeos-Sheefl 2 TTHIV Sept. 30, 1947. E, LABIN ET AL 2,428,118

PULSE MULTIPLEX SYSTEM Filed April 7, 1944 '7 sheets-sheet s f 5 lof/H65 '5H/F751? 'C1/22a .Wa o 77M. Mom/nrw? WRF I u' iL/11a BY /I Sept 30, 1947. E. LABm Em. 2,428,118

PULSE MULTIPLEX SYSTEM Filed April 7, 1944 7 SheelZS-Sheerl 5 BYA /37 ATTORNEY l Sept'. 30, 1947.

E. LABIN ET Al.

PULSE MUIJTIPLEX SYSTEM 4Filed April '7, 1944 7 Sheets-Sheet 6 5457' "THM/N44 i @LIPPE/F BY @fj/eff ATM/w27 vSept. 30, 1947. E, LABIN ET AL PULSE MULTIPLEXYSYSATEM 7 Sheets-Sheet 7 Filed April '7, 1944 Paten'tecl Sept. 30, 1947 ZZtilt PULSE MULTIPLEX SYSTEM Emile Labin, New York, and Donald D. Grieg,l Forest Hills, N. Y., assgners to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application April 7, 1944,k Serial No."529,9313

This invention relates to multi-channel communication systems and more particularly to multi-channel transmission Aor broadcasting and selective reception of transmitted channels.

. One of the objects ofthis invention is to provide a method and means for multi-channel communication or broadcastingv over `a common` transmitting medium such as a transmission line or a given carrier frequency Wave, as the case may be, the different channels being distinguished by different identifying characteristics or signals.

Another object of the invention is to provide a method and means at receiving points for selectively detecting any one or more of a plurality of lsignal channels transmitted in timed spaced relation over a common transmission medium such as a transmission line or on a given'carrier frequency Wave. y

Additional objects of the invention include the provision of methods and means for multi-chan.-l nel pulse transmission and reception wherein y different characteristics of the pulses of one or more channels are modulated with different signals; and the different characteristics of Vthe pulses of a given channel are eitherseparately demodulated or are simultaneously demodulated by separate means for simultaneous reproduction.

According to certain features of the invention,v

the transmission of signals may be one-Way as in radio broadcasting, or they may be twoway as in multi-channel communication between tWo terminals whether or not the communication is over some form of transmission line or by radio link. The plurality of channels are each constituted by a series of pulses one characteristic of which is modulated With a given identifying signal different from the identifying signals of other channels, and further modulated according to one organother4 of a plurality of different principles of pulse modulation for transmission of intelligence. The several series of pulses are time controlled so that thepulses of the different channels interleave together to form a single train of pulses for transmission purposes over a common transmission medium to one or more receiving points. At each receiving point is one or more channel selectors adapted to select according to the identifying signals one or more channels and to demodulate the pulses thereof to obtain the intelligence of the respec-V tive channels.

.The identifying signal for each channel may.y

32 Claims. (Cl. 179-45) tic, such as width, amplitude and slope of leading and trailing .edges,or the time position or cadence frequency of the pulses by a signal different from-:the identifying signals of other channels. `lf desired, different channels may be identified by modulation of different pulse characteristics-,that it, the pulses of one channel may be given a'particularwidth modulation while pulses of another channel may be time modulated by' a'givenfrequen'cy signal, the identifying signals all being diiferent'from or outside of the frequency band of the message or other type of intelligence with which the channel pulses are modulated. 2

The. pulse .modulation feature of the invention may be'any know-n form'so long as modulation limits are chosenlso'as to not interfere with pulses of adjacent channels or the channel identifying signals. The type of modulation, for example; may be one of several forms ofl P. T. M.' .(pulse time modulation), or P. A. M. (pulse amplitude modulation) or any combination of the different types of modulation so long as one doesnot interfere with another. By differentv formsof P. T. M. modulation, reference is madetofsingle pulse time modulation with respect to a given time position or some pulse or pulses xed'in time position, and various forms of double'pulse time modulation such as where the successive pulses of a given channel are time displaced from'normal time positions in pushpull manner toward and away from each other.

Another form of pulse time modulation knownA as P. W. M. (pulse 'width modulation) may also be used, the leading and trailing edges of the pulses being displaced relative to each other Yin the manner of single or double pulse time modulation, asfthe case may be.

- Bythe term pulse applicants have referencev toY an electrical pulse of energy which may be modulated in one or morevof its characteristics,V such for'exa'mpleas its time position, width or duration, and amplitude. By the term channel applicants havereference to a channel of communication. (More than one channel of communication may.- be transmitted simultaneously by meansor the same pulses, the pulses being simultaneously modulatedwith more than one signal. Channel is also used in reference to transmitting and receiving channels in the transmitter and receiver, respectively.

The above andother vobjects and features of the inventionrvill become more apparent upon consideration of the following detailed description to be read in connection with the accompanying drawings, in which:

Fig. 1 is a block diagram of a multi-channel communication system according to our invention;

Fig. 1A is a graphical illustration of multichannel pulses used in explaining the operation of the system of Fig. l;

Fig. 1B is a block diagram showing a radio link arrangement that maybe used with the multichannel communication system of Fig.v 1

Fig. 2 is a schematic diagram in perspective showing the multi-channel communicating -system in the form of a radio broadcastingand relay system;

Fig. 3 is a schematic wiring diagram of the phase shifter, time modulator 'and ,pulse width shaper circuits for one of the channels of the system of Fig. 1;

Fig. 4 is a graphical illustration used in explaining the operationv of the circuit of Fig. 3;

Fig. 5 isa schematic wiring 'diagram Vof 'apuflse Width selector circuit of the 'character employed in receiving channels foi 'the system,

Fig. 6 is a graphical illustration used 'in explaining the operation Tof 'the :circuit oi Fig. 5';

Fig. 'l is a schematic wiring diagram of a form of 'P. T. M. demodulator 'thatmay .be vemployed in the receiving channels 'ci `thefsystem;

Fig. 8 is a graphical villustration used in. `eifrplaining vthe demodulating principle of the circuit of Fig. 7;

Fig. 9 is a block diagram `of a modiii'ed ."form of multi-channel communication system;

Fig. 10 is a graphical illustration used in explaining the multi-channel Aprinciples employed in the system --of Fig. 9;

Fig. 1l is a wiring diagram of 1a P.A. .Mfmodulator;

Fig; l2 is a block diagramof a receiver adapted to'select channels 'according :to differences in amplitude of the pulses of diierent channels;

Fig. 13 is a further modicationof the multi:- channel communication system; and

Fig. 14 is a 'graphical illustration ofthe?. F.. M. modulation .feature .of the system of Fig. 13.

Refer-ring 4to Fig. :1, a west terminal :l is shown provided with a plurality of transmitting channels three of which are shown. The three chan` nels include pulse ti-Ine modulators Hs, i12-and 2li, respectively, and also pulse Width Shapers or modulators t6, Il and 18. respectively.. The timing of the pulse modulators H, l2 and I3y is controlled by a base Wave :generator which is connected directly to the unit Il by connection 2l and through phase Shifters 22 and 23 'to the modulators I2 and I-3, respectively.

The pulse modulators maybe of any desired. form depending upon the principle Iof modulation. For purposes of illustrating this invention, the pulse modulators herein shown `are chosen of the "cusper type used for push-pullVl?. T. described Yin detail hereinafter in connection with Figs. 3 and 4.

The pulse width shaper circuits' f6, l1 Vand 'I8 may be `of any character suitable for -translating pulses or cusps into pulses of a desired Width. A circuit for electing this purpose is also shown in Fig. 3. It will be understood, however.' that the pui-ses may rst =be produced by a pulse generator vcircuit and 'thereaiter' modulated in time `by intelligence signals.

In Fig. 1A, a, train of pulsesicr channels I to -5, for example, is shown: by curve a. lIt will be understood, of course, that .a lesser num-berlor a ;ferent. channels, the vdifferences in Width fromV channel to vchan-nel may be in the order of one- `lfn'indredtlr -of Aa microsecond. Thus, a hundred of different pulse Width channels may be had with the v-n-ia-Xirnum Width Within one microsecond duration.

As shown by curve a of Fig. 1A, the pulses of different channels are distinguished by pulse width, the pulse Width Shaper for each channel being adjusted to provide va, pulse width different from the lpulses of other channels. While the Width 'of the channel pulses is shown to be progressively greater from channels I to 5, it will be understood 'that the identifying .pulse widths may be Amixed similarly as illustrated in Fig. l0 is that the wider pulses occur adjacent the -narrower pulses, thereby Yeconomizing on the required spacing between lchannels Where the centers cf the adjacent channel v`pulses are equally spaced.

The trai-n of channel pulses may be transmitted, as hereinbefore stated, by means of direct coilnection to the receiving terminals such, LAfor example, as east. terminal 3B by' Wire, coaxial. cable, etc., `or the two terminals may be interconnected by rad-io link as indicated by Fig. 1B. The train of transmitted pulses, for example, would be applied toan rR.--F. translator 24 whereby the pulses are used for modulating a carrier Wave `of ultra high frequency for directional or omni-directional transmission, .as the lcasemay be. The receiving terminal or terminals would be 'provided with an Elu-F. detector 34 for detecting the multichannel lpulse wave to video form. This detection applies channel .pulses .in video form, such as' shown yby curve' la in Fig. 1A, to the receiving channels which are provided with Width selectors 31,]32 and 313 and demo'dulators 36,31 and 38, respectively. The Width lselector 'is of lthe character 'adapted to pass only Vthose pulses ofV a selected Width, 'that is, Within 'close tolerance, and to reject all other 'pulses of different Widths. A circuit' of this Character 'is illustrated in Fig. 5, the details of which are described hereinafter. This pulse Width selection is illustrated by curves band c o'f Fig. 1A, wherein the pulses of curve by are. the vpulses of channel I and the pulses of curve Scare the pulses of channel 3.

With the pulses of the selected channel segregated from the train of transmitted channel pulses, ithe intelligence with 'which the pulses are modulated may be readily reproduced by a suitable fdemodulaftor. 'In the case of time modulation. a time demodulator of the character illustrated in Fig. I7, the details of which are vdescribed hereinafter, may be employed.

From the foregoing description, it will be clear that bythe lsystem of Fig. 1 a plurality of channels, each represented by 'a series of pulses modulated With a given identifying signal diierent from the identifying signals of the pulses of other channels, are produced. The pulses of each channel are timed with' respect to the pulses of" other channels to interleave and form therewith a single train of pulsesfor transmission over a common transmitting medium. Each of the separate series of channel pulses is modulated with intelligence separate from the identifying signal. The resulting train of-channel kpulses is transmitted either by direct connection or by radio link. Receiving circuits such as unit 34 or a combination of such Vunits as indicated by the multiple receiving branches of terminal 3i) are lprovided at one or more receiving points, either along the line of the direct connection or at various locations within the range of the radio link, whereby the pulses of any given channel may be selected and the others rejected so that the intelligence of a wanted channel may be obtained without requiring any special synchronizing arrangement between the transmitting and receiving points.

. Fig. 2 illustrates further the radio link principle of the invention especially when used for broadcasting purposes. The system preferably employs omni-directional radiating antenna 50 mounted at a high point within a given populated area such as at the top of the highest building of a city or on a tower located at some other high elevation within'the area. As shown in Fig. 2,

the antenna 5I] is mounted on a tower 5l located on the top of a tall building 52. The antenna 5U may be of any construction suitable for omnidirectional radiation, one example being of the type disclosed in the patent to A. Alford No. 2,283,897.

vEach channel of communication may be assigned to a particular studio located within the area of the broadcasting system and others may be assigned to certain national broadcasting chains. For purposes of illustration, live studios ls, 2s, 3s, 4s and 5s are shown associated with the main broadcasting station 52. All of the channels are broadcast in the form of pulses interleaved in a single train as shown in curve a of Fig. 1A. This renders it possible to broadcast a plurality of different programs from one high point at a given carrier frequency so that re.- ceivers located within the range of the station may be equipped with directional antennas such as indicated at 51%,V for receiver 55, arranged in alignment with the antenna 50. This directional receiving antenna 56 may be fixed in position and the tuning for different programs effected by pulse width selection or other means of channel selection described hereinafter. The receiving antenna, of course, need not be directional but for best reception with a minimum of reflection interference from buildings and the like, the directional type will in most instances be preferred. Furthermorey the directional antenna need not be Xed on one broadcasting antenna but may be adjustable for alignment with other broadcasting sources.

In addition to' the selective reception of the broadcast from station 52, the multi-channel transmission therefrom may be relayed by radiolink through repeaters 6I, 62, etc., to a second broadcasting tower 65 in another city. The tower 65 is provided with a similar omni-directional radiating antenna 61 whereby the multi-channel train of pulses is broadcast for local reception. Should the receiving antenna B6 of tower 65 be within visual alignment of the antenna 50, the repeaters 6l and G2 would not be required since the antenna 6B would, in that case, receive the broadcast directly from the antenna 50, It will be understood, of course, that the .carrier frequency of the different broadcasting stations may be different where there might be overlapping of.

reception between the two broadcasting stations'. Where the omnidirectional broadcasting stations are far enoughapart that there is no overlapping, then the same carrier frequency may be employed but,'in that case, a different frequency forsuccessive repeater towers would be necessary as indicated by the frequencies F1, F2 and F3. .ForV further understanding of the radio link feature, reference may be hadV to applicants copending application entitled Broadcasting systems, Ser. No. 529,932, led of even dateherewith.

Fig. 3 shows the circuit of one form of P. T. M. modulator Ila such as may be employed at ll, l2 and I3, Fig. l, together with Ya phase shifter 22a of the character used at '22 rand. 23 and a pulse width Shaper la of the character'that'may be used at I5, l1 and lf3.V The phase shifter 22a comprises a condenser-resistor network CR1R2,

the relative values of which determine the phasev shift of the base wave 'lil applied thereto from base wave generator 20,'Fig. 1. Assuming that there is no phase' shift of thebase wave 'Hl required as in the case of channel l, Fig. l, thenv the wave may be regarded as of the phase posi;

tion indicated in curvev 4a of Fig. 4 when applied to primary coil 12 of the coupling trans-rv ties the wave '10, curveV lia, Fig. 4 to obtain a cusper wave 80, curve 4b. Time modulation of the cusper wave is produced by applying the signal intelligence over input connection 82 to primary coils 83 and 84 on the transformer 73. The signal intelligence operates, in effect, to vary the wave I0 relative to its zero axis as regards the full-wave rectification. This relative variation between the wave and the zero axis thereof is illustratedin curver 4a by the upper and lower modulation limits 8B and 8l. When the input signal varies the relative relation between the zero axis 61 and the wave 'lll asindicated by limit 86, the cusper wave is displaced as shown by the broken line 89a and Vwhen displaced to the opposite limit 81 by broken line 89h. It will be observed that the signal wave may `vary the cusps 9 l, 92, 93 and 9d in push-pull manner toward and away from each otherthereby decreasing or increasing. the time interval between successive cusps.

For transmission purposes, the cusps are clipped nected together and the cathode of tube |01 is connected through coupling condenser 93 across the load resistor IEM of the modulator lla. The cathode of diode lill is connected through a resistorv 06 to a potentiometer lll'l. The plates of the two tubes are connectedthrough a resistor lila to a second-potentiometer ISS. The cathode of the tube i792 is connected through a resistor' wlltoground. y

Such a 7. Thetwo diodes IDIl and: |02 operate'together asl aigatef clipper forclipping the cusper between limit: levels.v III'I and H2', curve 4b, the width of the gatel being controlled by the adjustment of potentiometer HIT and; the position of the gate relativeto the wave is'controlled by adjustment of: the potentiometer` |09;- The. gate position of the clipping. levels I I I and; I I2; onwave 80, curve 4b,- forexample, produces a pulse of the width W1, curve 4d; Thepulse: of curve 4d is shown to beiampliiied, it beirrgiunderstoodA that the pulse widtl'r Shapers: It;V IILand I8y may include one or more ampliiyingstagesinaddition. to the double diode circuitshownat |6a in Fig.l 3. By adjusting the potentiometerV |09', the gate levels I'and I I2 may be` shifted. tovpositions i'lla, H201; as indi-` cated oni wave IIIi', curvel 4c; The wave I|6` is identical tothe Wave ll'except: that it is shifted in, phase according to thevalues of the phase shifter: 22asuchas required by channel 2 or channellfiasthe oasemaybe;- Adifferent adjustment Ofsi the potentiometer |109' for'the wave IIB may providea. gates clipping at' a much lower level than thegate positions. IIli-and |:I2f oi curve lib.' lI-his results inithe pulse WidtliWz which is greater thanzthe .width Wn. It'. will thus be clear that by proper' adjustmentof the potentiometer |09 at the. pulse Vwidth shapers'of the different channels thatthe pulsesof the diierent channelswill have different pulse widths thereby identifying .the channelrepresentedby such pulses.

For: further understandingA of the cusper type of :modulator and?. the double diode clipping circuit, reference: may behad to applicants co'- pending: applications Serial: No'. 455,897, led August 24, 1942, and Serial' No'. 437,530', iiled April 3; 1942;. respectively..

The phase adjustment of the wavel '|0to position 10c, curve 4a, is'indicative of the time control of the pulses of the different channels, the phase position. ofy curve-10 represents the time control forfthe'pulses'of channel Iwhile the phase position 'iila'represents the time-control of the pulses ofi channel 2i, for example, thereby producing a cusper wave IIISI'which is displaced in phase with cusper.v wave- Slt-so'. that the pulse outputs of the two` waves. are diiere'ntly timedv for interleaving eis-indicated' by curve dd As hereinbef'ore described in connection with Fig;.1A,.the:pulses-of` the different channels are identiiiedlby different pulse widths and are timed diierently so that they interleave to form a single train of pulses as shownvby curve a, Fig. 1A. This trainoi channel pulses is transmitted over a commonY transmission medium either in the form of a direct line connection or radio link to the east terminal'in the case of a multi-channel communication system, or to-separate receiver units constructecl' along the lines of'each receiving channel of the terminal where the transmission is by radio link andtlie transmission is omni-directional. as in radioy broadcasting.

Figs. 5' and 6' illustrate a pulse Width selector circuit of the character disclosed in applicants copending application, Serial No. 487,072, led May 15, 1943, that may be used in each channel receiver ofy the east terminal, or in individual receivers: for selective reception of the channels where multi-channel'broadcasting is performed. The circuit includes limit clippingl stage as anlinputcoupler which limits all input pulses to substantially the same amplitude, and also inverts the-.input pulsesifrom a positive polarity as indicatedby the pulses of curve 6a to negative po-I larity as indicated by the pulses of curve 65, Fig.

6'; This output pulse energy from sta-ge |2|l`fisV4 applied through aresistor R toa shock excitable- L-C. circuit |25'. Connected across the tunableV circuit |25 is a vacuum tube I 3|), thecathode |31' of which is connected to the input sideV of the circuit |25, while the anode |32is connected to-y the opposite sidel |33of the tunable circuit. Theside |33is also connected toal source of anodeI potential |34. The pulse energy, curve 6b, from the anode connection |28 is applied to the grid |35 of the tube |39 so as to block the conduction-1 between the cathode I3| and the anode |132-whilepulse energy is applied to the circuit |25;- Thel undulations produced in the circuit |25' inv re-- circuit |25 is tuned for selection of pulse width..

W3. Curve 6c represents theoutput of the cir cuit |25 when the circuit is tuned for selection: of pulse width W3, illustrating the different out;` put undulations for the different pulse widths'of: curve 6a. When the leading; edge |5| -of thepulse W3 is applied at negative polarity as indicated.lv by curve 6b to the circuit |25, an initialundul'ation |52 is produced. which isA normally followed by undulations |53, |54 andV so on'in the formofI a damped wave. When the circuit |25 is tuned4 to a frequencythe period of which is` exactly twicei the width W3, the the initiated oscillatory energy crosses the zero axis from undulation |52 to,v undulation |53. Since theI trailing edge |56 shock'excites the cir cuit in the same. direction at this point, thelundulation |51 produced thereby in'vthe circuit |25 adds algebraically to thel undulation |53 to pro-l duce undulation of undulations produced by the leading and trailing edges of pulse width Wa would normally tend to produce a negative undulation |'6 I which would continue as a damped wave as indicated at |62'. The damping tube |30, however, eliminates the trailing oscillations |62l so that they do notinterf fere with the undulations produced by subsequent pulses applied to the circuit |25.

A pulse width less than pulsel widthI Was/uch.. for example, as pulse widths W1 and W2, will not produce maximum undulations asv great as the undulation |60 for thetuning adjustment corre-l sponding to pulse width W3. This is illustrated by the undulation-s and |`|2` produced in response to the pulse widths W1 and W2, respec`V tively. The reason for thisis readily apparent because the shock excitationsV produced by the leading. andtrailing edges ofi the pulses of lesser widththan Wa are inpart opposed to each other as indicated by thebrok'en lines associated with the undulations IJI and |12." Theundulations |14*r and |15 produced in response to the greater pulse widths W4 and W5 are likewise smaller than the undulation |58 since here again the oscillations produced in response to thev leadingl and trailing edgesof the greater pulse widths are in part opposediftoeachothersothatthe algebraic summationtl'ereof'v isv less than" in the case ofY In the output |48 of stage trailing edge |56 occurs where,

|60. The next succeeding pairs- 'the 'undulations produced in response to pulse width Wa.

" vThe threshold clipping stage |45 is adjusted to .clip vat a level |16 thereby obtaining and amplifying the crest portion |68a of the undulation |88 as indicated by curve 6d. The pulse shaper |58`is Vpreferably of the character adapted to differentiate the pulse |60a producing the pulse shape |691) of curve 8e. The shaper also preferably Vincludes a clipper stage for clipping the positive pulse portion of pulse shape |681) at level |18 thereby producing a narrow width pulse 188e synchronized in time to the pulse of widthA W3. Thus, any time modulation applied to the pulses of width W3 will carry through to the output 'pulse |690 which may be demodulated to an audio wave by the demodulator 36u, of Fig. '1. It will also' be readily apparent` that by adjusting the tuning of circuit |25 to another frequency 'the period of which is twice the duration of any one of the other pulse width's of curve 8a, thata corresponding output pulse will be produced representing the pulses of the pulse width selected.

Fig. 7 shows one form of P. T. M. demodulator that may be used as the demodulator at 36, 31 and 38. in the receiving channels in Fig. 1. The demodulator has two parallel input connections |8I and |82, connection |8| going to a coupling amplifier tube |84 and connection |82 to the con- Atrol grid |94 of a demodulator or mixer tube |83.

The output connection |85 of the tube |84 is applied to a resonant circuit |86 which is tuned to th'e repetition frequency of the pulses of the ,channel passed by the width selector 3|, for example. The pulses from the tube |84 shock excite ,the circuit |88 into resonance at the tuned frequency producing an oscillatory wave |81. This wave is twice the frequency of the base wave 19 employed at the modulator (Figs. 3 and 4). To

obtain a fundamental wave |88 corresponding to the wave 19, the wave I 81 is applied to a frequency divider |89.

Either the wave |81 or the fundamental wave Y|88 may be used for demodulation purposes, but Aan odd harmonic of the fundamental wave |88 is preferred. It is also desirable, where the degree of T. M. is a small proportion of the period between pulses, that a high odd harmonic of the fundamental wave |88 be provided for demodula- `tion in order'to obtain an appreciable variation in amplitude for small changes in time displacement. The fundamental wave |88, therefore, is `vapplied to a frequencymultiplier |98, Fig. 7,

whereby the desired odd harmonic wave |9|,V (see Fig. 7 and curve 8b Fig. 8), is obtained. While wave |9| is shown for purposes of illustration to be the third harmonic yof the wave |88, a higher odd harmonic may be preferred in some cases.

A phase shifter |92 is provided in the output of the frequency multiplier to shift the demodutember 28, 1942, and N, H. Young, Jr., Serial No.

517,160, filed January 6, 1944. l

In Fig, 8, .curve 8a represents the pulses of a particular channel selected for demodulation such las channel The pulses of curvev 8a are time displaced according to a linearly increasing signal input, the broken line positions indicating the lnormal timing of the pulses in the absence ofl a -modulating signal.

The grid voltage wave |98 of curve Bb'indicates the Aharmonic wave |9| ap- 'plied to tube |83 from the phaseA shifter |92. The

resulting grid potential produced in the tube |83 bythe inputs on grid elements thereof is indi'- cated by curve 8b.A The wave |98 represents potentialenergy of the selected odd harmonic wave |9| together with the pulses of curve 8a. The polsitionsof ,the pulse potentialsA on the curvev |96 are determined by thedegree of time modulation of the pulses. For zero modulation asl represented by vinput pulse Ih, a'given grid voltage condition isproduced. The time displacement, either forwardly or rearwardly with respect to this givenV grid voltage condition, controls the positionof the 'pulse vpotentials onthe slope of curve |96. Forv displacement due to a signal of negative polarity vsuch as represented by the displacement of pulse la, the corresponding grid pulse potential in'curve 8b assumes a lower posiltion on`V the curve V|98 than the grid pulse 'potential vcorresponding to pulse |b the position of which represents zero modulation. For pulses having displacements due to signals of. progressively greater positive polarity, such as pulses |c, |d, etc., th'e corresponding grid-pulsepotentials thereof in curve 8b occur at progressively higher pointsonthecurve |96. Y

The bias on the control grid |94 ofthe tube |83 is selected so as to provide a threshold clip- I'ping level |91 which clears the amplitude ofthe wave |96. Thus, the output of the tube |83 cornprises atrain of pulses |98, wherein the pulses are modulatedin amplitude according to the time displacement of .the corresponding. grid pulse '1potentials.. .Thepulses of train |98 denne an envelope |99 which correspondsto the rsignal energy at the transmitting station.4 By applying the am- -plitude modulated pulses of curve 8c to a suitable filter .20|, the signal wave represented vby enzvelope|99 vis detectable on earphones '292.

In Figs. 9 and 10 another form ofv multi-channel communicating system is illustrated wherein the pulses of each channel aredoubly modulated -With intelligence in addition to the channel iden- '.tifying signal. ":The double `modulation of. the

pulses lmay be utilized to provide ydifferent tone effects on the same program or for other pur- .po'ses such as television. Branch; channel la:

vintelligence may, for example',"carrythe sound .effects produced at one microphone in the studio 'while branch channel Iy modulation carries the tone eiects as'received at a second microphone differently located from .the rst microphone.

ABy segregating lthe vtwo branchl channels at the same receiver Vandl applying them to different speakers, the desired tone effect will be reproduced. This dual tone transmission may be carried even further by adding additional branch channels onvthe samecarrier pulses of a main channel or by utilizing a separatemain channel 'such as branch. channels 2a: and 2y for conveying the tone eiects produced at still kadditional points within the same or another studio to separate speakers at the receiving point.

The transmitting channels of the system of Fig. 9 are substantially the same as those'illustratedin Fig. 1,`like reference characters beingl used for like units. Theroutput pulses of the pulse width Shaper |6, for example, are fed to a P. A, M. modulator y2|i|ly which may be of the 'character shown in Fig. 11 hereinafter described.

The pulses of main channel are thus both -ldulateq time. Position. anqmlllmd 312W the. 'intelligence of. hr'rlh .energies im 'sedile 155.94m@ 'that VE? 'z mai@ .trallllml Qha'nngl vare provided .at -the transinit-.ting Qterrninail,.ithe `channel pulses 1would appear; substantially-.as shownincurve 10o, Fig. 10m Iyhe channel pulses .are shown to be amplitude modulated, the channel l pulsesbeing furtheipmodulated-timedisplacement in push-pull manner relative to` their `normal positions shown-in, .broken lines 204. VCurves l0b and I Qcillustrate the demodulation Aof the Atwo diierenttypesof modulation for the pulses 0f Channell'. y

Whileamplitudex3modulation hasjheen added tothe time modulation on the same pulses, it will bev clear that other shape characteristics such `as Width and'slopeuof leading vand/or trailing edges may also be 'employed 'for other messages- `In cases of amplitude andtimemodulation-of the :same pulses.; some ,.iCross-talk" may result :unless the' leading arid/0rk tralingedges. of `the .pulses are maintained s substantially vertical. .Such cross-talk however;v caribe greatly minimized by using a. peak riding-clipper, or .by

diierentiating 'the pulses vat the Yinput Vof the MP. T. demodulator. :Peak riding clippers/are 4shown. for this Ipurposein Fig.'9 vand .the receiver unit'zsar'igis. .v

It is also contemplated, where .desirable, Vto use the P. A. M. modulators to apply 'identifying signalsto the pulses ofdifferent channels. The vP. 'A.iM. modulators may be employed to give thepulses of .each 'channel a: distinguishing amplitude 'different from .pulses fofzother. channels similar to thefidentifying pulse' widthfeature.

suitably shaped at A224 and. applied toa deblock- Ving mixer assimiler rofmrxer tube lisa ef Fig.

thereby providing-attain lof pulseslwhich va-r'ies in amplitude according to theA. M. modulation at the transmitter. This pulseoutput is .ltered at 229 whereby the pulses Vlare removed -and `the envelope .'Wave'thereof applied to earphones 230.

Referring back to the PfA. M. 'modulatonll of Fig. 9, Fig. V11 shovvs one type of circuit vthat may be used. It includes agridcontrolled vacuum tube 240 to which T.=M. pulsesareapplied over connection 24| and; an audio signal-Wave is applied through to vtransformer-242 and resistor 243. The secondary coil 2M of the transformer is'connected to a negative source of poten-tial C- whereby thetube v2li() is operated beyond cut-ofi. The audible signal wave varies'the` negative '-bias thereby altering, accordingly, the amplitude v'of the Ypulseconduction of thetube. The yamplitude modulated output is indicated by pulse train *245.

Fig. `1-2 showsa receivercircuit along the lines ofthe l,Discriminator circuit disclosed inthe copending application =of:.D. D. Grieg, Serial No.

.The train of .channel pulses 'shown by. curve Illa is transmitted jeither by. :direct .line .connection or .by radio 'link to :theJeceivingfpoint-or points. -The 'east te'rminal iszshown to be provided with 'two main .receiving .channels l V4and 2 each having two branch fspe'akers. :The receivingchannel ll, orzexample. is-shown tobe provided with a pulse :width :selector 121.0 "of the .same character .used :in the receiving channels 'of the system 'of Fig. 1. The 1P. T.`"M. demodu- .latorfeature of channelilrreceiver issubstantially the. same as .shown AinfFig. 7. like 'reference characters .designating corresponding parts. The out'put .pulses tof :the selector 1 2 l 0 :of4 a selected channel v'are applied :to 'the :base Iwave gener- 'ator 2M Which;.incl`udesthetcircuits of units 1.8.4,

Il 86andl89 in Fig. 7, :the base Avvavc,output,2I6 .Ccurve Illb) corresponding:togwaveld in Fig. .7. The 'frequency multiplier ISU `produces 'the .desired'harmonid either;.evenaor odd, Whichlis thenapplied. through phase shifter l92gto the mixer [83. VThe 'demodulationoi 'thepulsesof channel lpassedv byfselectorfll areclipped by peak riding 'clipper 212 .and y:then Ydemodulated ini the same manner-'described in connection with curve -8b of Fig.v 8. 'The time-displacement of thepulses of .channel-fl' is .according to a linearly decreasing signal `as indicated by the envelope 220 defined by thepulse'output 'of-:tube |83 operating at threshold clipping level 2|8. The iilter 22! removes the-pulses and Aapplies the envelope wave to earphones 222. f

As hereinbefore stated, the peakriding clipper `2l2 minimizes the crossetalk -introduced into the time modulation -channel byamplitude modulationof the samepulses Variations in slopedue to amplitudemodulation arethus not carried intoY themixer H33. The baseawave produced by generator 2M isalso used for producing'deblocking pulses 225, curve lc. AThewave v"channel such Ias channel `3. -Iireieraloly includes an amplier' stage arranged -to Yindicated at 24513.

487,071, filed May 15.51943, for selecting channel -pulses when they are 4distimguish'ed 'from channel to channel by diierent amplitudes. The train of channel pulses (1,'2, 3,`4 and Y5) `is'iirst threshold clippedby'clipperZdE ata level 245e just exceeding the 'amplitude of the pulse V'of 'the wanted The clipper 245 invert and amplifythe clipped pulse portions V'as The pulse train is mixed with the inverted `pulses. nofyvave 24'5bi'n`mixer '2`4`6 whereby the inverted pulse portions substantially eliminate or at least reduce'the amplitude of the V"pulses of amplitude greater than the wanted vpulses to alesser value; Bythreshold clipping the remaining pulses by clipper 241 at levelc,

the pulses-ofthe Wanted channel 'are thus Lobtained asjindicated by 'Wave r`2118. The clipper circuits 42155l and 241Lmay 'be made adjustable for "selection 'of .diiierent channels or they may be 'arrangedtoclip at predetermined levels for the 'selectionoi pulsesof a'given amplitude. A

`InLl'igs. 13 and 14a' further' multi-'channelcoml'municat'ing l system is illustrated showing Vthat another type of time modulation 4may be substituted -for .the time modulation of'a, channel 'heretofore ldisclosed 'aridi that theresulting pulses may also be amplitude modulated. .This embodi- .nient further-demonstratesthe use .of channel vso .identifyings'ignals other than pulse Width and 'aise'.,tnat bbtnjtypes {of .identifying signals may he used the same ymulti-channel transmitting ,aridreceiving systems. The transmitting'channelsjof the Isystem of Fig. `13K-are similar tothe .tofbe an M. type ofmodulator.

jtransmitting `channels of Fig.` 9,7m fact, channel '3 -is Vshovvnjto be identical, Channels! kand however,- different in the type of modulation and channel I differs furtherinthe typeof channel identifying signal. `Referring particularly to transmitting channel-1,` theI 'modulator 'is chosen Any known frequency modulator-'such .as-the rea'ctance oscillator 'type lmay he used for 'modulation-of intelligence of branch channel `I 1v. Ihe-base or syn- .chronizing Wave forti-iis typeof modulation is produced `vby a stable type of wave generator'ZU common to all of the transmitting channels the same as in Fig.J 1. The'base `wave, however, lis

Igence applied over the branch channels.

sulting pulses are thus modulated with respect to theirv cadence or repetition rate according to the intelligence applied to the modulator 256.

`j'ilhese pulses may be applied to a P. A. M. modulator 266 in the same manner shown in Fig. l1 whereupon the pulses are amplitude modulated according to the intelligence of a second branch `channel ly.

The pulses of main channel are characterized by a channel identifying signal which is a frequency signal f1 from source 25| preferably selected outside the frequency band of the intelli- This identifying signal may beof a frequency tone within the band but, in that case, a filter must .be provided to lter out the corresponding frequencies from the intelligence applied over the branch channel ly and other channels employing this type of modulation in order to preserve the identity of the identifying signal.

Main channel 2 is also shown to have an F. M. modulator 255 but in this case the base or synchronizing wave applied thereto is shifted in phase by phase shifter 254 relativeto the Wave applied to the modulator 256 of main channel I. The identifying signal for this channel is that of pulse width produced by the multivibratorshaper 256, the multivibrator feature thereof bev ing adjustable to produce pulses of adesired width. This pulse output may also be amplitude modulated by a separate branching channel 2y at 266. f

The transmitting elements of the main channel 3 is the same as those of channels and 2 of Fig. 9 and therefore need not be described.

The train of pulses produced by the three main transmitting channels is shown by curve Mb in Fig. lll. i These pulses are translated to radio frequency at 266 for transmission to receiving units 265, 266, etc. Receiving unit 265 is shown to include an R.F. detector 261 whereby the pulses 'are detected to video form as indicated by pulse train 268. blocking selector 269 which normally blocks the pulses except when a deblocking pulse is received from a generator 216. The generator 216 is adjusted to provide blocking pulses at a normal pulse timing slightly greater than the interval spacing of the pulses of any one channel. The pulses of the successive channels are passed by the deblocking selector 269, clipped by peak riding clipper 211 demodulated to audio by the demodulator 212. The signal filter 213, however, passes only the identifying signal, so that a selection rotation continues throughout the train f channel pulses until the proper identifying signal is received. Upon receipt of the identifying sigbranching receiver circuit of the receiving unit `265. The pulses of channel l as shown at 216` are applied over line 296 to decoupler amplifier 29| and thence through filter 292 to earphones 293 for reproduction in the above manner.

From the foregoing, it is clear that an identifying signal other than pulse width and amplitude may be used for receiver selection of a particular channel from a train'of channel pulses. Where the P. A, M. is used for modulation of intelligence, it may also be used for applying a given frequency signal for identification similarly as where such signal is applied to P.' T. M. and P. F. M. modulators. y

Receiver unit 266 is similar to the channel receivers of Fig. 9 except that an R.F. detector 366 Ais shown, and the P. T. M. demodulator is replaced by a demodulator 362. This unit is provided With a pulse width selector 36| for'selecting those channel pulses which differ in pulse width. Since the pulse width selector removes the amplitude modulation of the pulses as indicated by the cording to width is shown at 363 to be channel 2,

These pulses are all applied to denal, the deblocking pulse generator is synchronized to the repetition rate of the pulses of that channel thereby locking the oscillator 216 into step, the selector 269 being thereafter deblocked in proper time as indicated by the deand the same channel is shown also selected by selector 364 according to curve 361, the type of selection here being such as to preserve the amplitude modulation as indicated at 309.

-To illustrate further the fact that this type of time modulation may be applied to pulses in a `multichannel system, the pulses of channel I in curve |417 are shown modulated according to the principles of'this type of modulation by a signal wave 326 shown by curve Ma, Fig. 14. The limits of pulse displacement according to the principles rof this type of modulation are selected so that the modulation will not interfere with the pulses of adjacent channels. The modulation of the pulses caused by the signal 326 is indicated by the broken line positions of the pulses of channel Assuming that a normal interval of T exists between the pulses of channel l in the absence `of modulation, then as a positive signal is applied as shown at point 32| on wave 320, the pulse corresponding to such instantaneous signal value will be spaced from the preceding pulse by an interval T-l-At. Should the signal value increase a corresponding amount from point 32| to 322, the interval between the channel pulses occurring at these two points is T+2At. At the next point 323 of pulse occurrence on the curve, the signal yvalue is shown to be the same as at 322, therefore, the interval between points 322 and 323 will also be T+2At. A decrease in the signal value to pulse recurrence point 324 will decrease the interval proportionately as indicated by the interval T-l-At. Since the next pulse occurrence point 325 is substantially at zero signal value, the interval between points 324 and 325 will be T representing zero potential for the signal. A swing of the signal in the negative direction causes the intervalsbetween pulses to decrease as.- snownifor the'negativeportion 32M of the :"si'gnal wave. During vthis oscillation-ofthe signal zwave, V:it 'will be noted that .the lpulse spacing Ilca'uses Ythe `pulsesto loe displaced -from normal :positions throughout the cycle until the wavesrc- "turns to the zero center line $40. `By controlling the limits of signalswings for by limiting the degree oil". M. modulation ofthe base wave at ithe -transmitteig f the pulses can be maintained zwithin rtheallotted limits betweenpulses of adjacent channelsinv the train of pulses.

fIt Will'be readily apparent Ifrom the foregoing -description'fthatour invention is applicable for transmission lof a plurality of programs on the .same .carrier .frequency and also that dilerent programs or different parts of the same program -(diiferent soundefectsior example) may be carfried 'by the same pulses; also that various types Kof pulse modulation and synchronizing signals rmay .be employed.' Further, ywhile in existing '.'broadcasting .systems programs are generally Atnansmitted forvoice and 'musical programs, other `typesofwintelligence may also'be transmitted. For example, pulses may be transmitted in this -manner'sas'iacsimile signals, the-pulses being used f {directly as the facsimile build-up characters. The .transmitted pulses Vmay also constitute a sound itrackfor television as Well'as synchronizing pulses :required forcontr'ollingtheline and frame scanning in facsimileand television transmission.

VWhile Wefhave-described `above the principles :ofour inventioninconnection with specific ap- .paratus and vparticular vmodifications thereof, it -is to he clearly understoodthat this description is :made only bylway of example and not as a limitation on our invention and the scope of the ac- .companyingclaims Y "Wexclaim: 1. "A method of `multi-channel communication comprising producing a `separate series of pulses for each of aplurality of channels, modulating the'pulses of each'channel with a given identify- .ing'signal difierentirom the identifying signals .of thepulses ofV other-channels, timing differently :the pulses 'of thediiierentchannels to interleave thedifierentseries ofr pulses together as a -single itr'ain of pulses Afor,transmission over a common transmitting medium, modulating a .characterisdaicof the 'pulses of :each `channel according vto instantaneous signal .values of.an intelligence ex- :clusive ofN the Aidentifying signals of said channels, fandftransmittin'g said train of pulsesover said ,transmitting medium; andyzat a 'receiving point, segregating from `saidtrain 'those pulses having Vthe -identifying 'signal .of a given channel, .and demodulating the segregated pulsesA to :obtain the intelligencewith which they are modulated.

Y `2. :A'methodaccordingftoclaizn `1 wherein the kidentifying signal" modulation vof Veach "channel includes Width .shaping the` pulses of each .channel tofa` width diierentfrom 'the Width of the :pulsesof other channels,`

23. fA method according to claim l wherein the :identifying signal modulation of each v`channel includes amplitude; modulating 'therpulses 'of each .channel to anamp'litude different from theram- .plitude -oi" the pulses of other channels.

A method according .toclaim l wherein the .identifying modulation of'each channel includes Kmodulatingthepulses `of each .channel with .a signal of a frequency-outside of thefrequency 'band of the'intelligence with which the channels .are `modulated and which differs I'from the frequency ofthe. identifying signals with which the .pulses of other lchannels arern'o'dulated.

.transmitting medium;

Ynel according .to a second "5. A=method -accordin to claim 1 wherein'the Ymoitlulating-operation includes modulating a first characteristic of the pulses of one channel according to one intelligence and modulating a -second characteristic of the-same pulses of said one `channel according to another intelligence;

"and the demodulating operation includes demodulating the pulse energy of said given channel to iobtain the intelligence with which the rst charthe pulses of each channel with a given identifying :signal .dilerent from the identifying signals -of the pulses of other `channels'timing differently -the pulses .of the .dilerent channels to interleave the different series of pulses together Yasa single train `of pulses for transmission over a common transmitting medium, modulating with intelligence one characteristic ofthe pulses of a first channel, modulating with intelligence a second characteristic of the pulses of a second channel which is diierent from said one characteristic, and transmitting said train of pulses over said and, at a receiving point, Yselecting the pulses of said rst and said second channel from V,pulses of other .channels according to Atheir identifying signals, demodulating the pulses of said rst channel according to one principle of demodulation to obtain .the intelligence with whichsaid one characteristic is modulated, and demodulating the pulses of saidsecond chan- V principle of demodulation to .obtain the intelligence with which .said second characteristic is modulated.

1I. A method Yof multi-channel transmission comprising .producing-a separate series of pulses for each of -a plurality .of channels, modulating the vpulsesof eaclrchannel with a given identifyingsignal different `from the identifying signals o'f.the;p\.llsesrof` other channels, timing diierently ,thepulses ofthe diiierent channels to interleave the ldiierent series of pulses together as a single .train of pulsesior transmission over a common .transmitting.medium,. modulating a characterictic 'f .thegpulses' of each` channel according to instantaneous signal .values of an intelligence exclusive f .the"identifying-signals of lsaid channels, and transmitting. said train of pulses-over a common ,transmission medium,

'18. A .method according .to claim 7 `wherein the transmitting operation includesltranslating the pulses of said traininto carrier. frequency pulses ofagivenfrequency and transmitting saidl carrier'frequencypulses. '9. 'A'method according to claim V'l 4wherein the identifying signal modulation of each channel in- .cludes'width shapingotthepulsesof each channel to aLwidthdiferent iromthe -Width of the pulses Aof;other channels,

'10. Amethod according to claiinl' wherein the identifying signal modulation of each channel includes'arnplitude modulating the pulses of each channel to'anamplitude different from the amplitudejof'thelpulses of other channels.

*il l. IA method according to claim 7 wherein the identifying modulation of each'ch'annel includes modulating the pulses of each channel .with a signalof a frequency 'outside fof the frequency bandothe intelligence with Which'the channels are modulated and-Which differs fromthe frequency of the identifying signal with` which the pulses of other channels are modulated.

12. A method according to claim 7 wherein the modulation operation for at least one of said channels includes modulating a first characteristic of the pulses of one channel according tov for each of a plurality of channels, modulating the pulses of each channel with a given identifying signal different from the identifying signals of the pulses of other` channels, timing differently the pulses of the different channels to interleave the different series of pulses togetherv as avsingle` train of pulses, modulating with intelligence one characteristic of the pulses of one of said channels, modulating with intelligence a second characteristic of the pulses of a second of said channels, which'is different from said one characteristic, and transmitting said train of pulses over a common transmitting medium.

14. A method of selectively receiving a given channel of communication from a multi-channel train of pulses wherein the pulses of each channel differ from pulses of other channels by a different identifying signal with which they are modulated, comprising segregating from the train of channel pulses those pulses having the identifying signal of said given channel, and demodulating thesegregated pulses'to obtain the intelligence with which they are modulated.

15. A method-according to claim 14 wherein the pulses of one of said channels is doubly modulated, that is, a first characteristic of the pulses is modulated according to one intelligence and a second characteristic of the same pulses is modulated with another intelligence; and the demodulating operation includes demodulating the pulseenergy of the doubly modulated channel according to one principle of demodulationto obtain the intelligence with which said first characteristic is modulated, and demodulating the pulse energy of said doubly modulated channel accordingto a second principle of demodulation to obtainlthe intelligence lwith which said second characteristic is modulated. f

16. A -multi-channel communication system comprising separate means for producing a series of pulses for each of a plurality of channels, separate means for modulating the pulses of each channel with an identifying signal different from the identifying signals of other channels, means controlling the separate pulse producing means to time differently the pulses of the different channels to interleave the different series together as a single train of pulses, means for modulating a characteristic of the pulses of each channel according to the instantaneous signal values of intelligence exclusive of the identifying signals of said channels, and means for Itransmitting said train of pulses over a common transmitting medium; and means, at a receiving point, for segregating from said train those pulses having an identifying signal at a given channel, and means to demodulate the segregated pulses to obtain the intelligence Ywith which they are modulated.

17. A system according to claim 16 wherein the separate identifying signal modulating means includes means for width shaping the pulses of its respective channels to a width different from the pulse widths of other channels.

18. A system according to claim 16 wherein l 18 the separate identifying-signal modulating means includes means for amplitude modulating the pulses of its respective channel to an amplitude different from the pulse amplitudes of other channels.

19. A system according to claim 16 wherein the separate identifying signal modulating means includes means for modulating the pulses ofits respective channel with a signal of a frequency outside of the frequency band ofthe intelligence with which theV pulses of such channel is modulated and which differs from the frequency of the indentifying signal with which the pulses of other channels are modulated.

20. A system according to claim 16 wherein the means for intelligence modulation of at least one of said channels of pulses includes means to modulate a first characteristic of the pulses according to lone intelligence, and means to modulate a second characteristic of the same pulses with another intelligence; and the demodulating means at the receiving point includes means to demodulate Vpulse energy of the segregated pulses according to one demodulating principle to obtain the intelligence with which the first characteristic is modulated land means to demodulate pulse energy of the segregated pulses according to another demodulating principle to obtain Athe intelligence Vwith which the second characteristic is modulated.

21. A multi-channel transmission system comprising separate means for producing a series of pulses for each of a plurality of channels, separate means for Vmodulating the pulses of each channel with an identifying signal different from the identifyingl signals of otherchannels, means `for modulating a characteristic of the pulses of each channel according to the instantaneous signal values of intelligence exclusive of the identifying signals of said channels means controlling the separate pulse producing means to differently time the pulses ofthedilferent channels to interleave them togetherv as a single train of pulses, kand means for transmitting the interleaved channel pulses over a cormnon transmitting medium;Y

22. Av multi-channel transmission system according to claim-21 wherein the transmitting means includes means to translate r.the train of pulses into carrierfrequency pulses of a given frequency andmeans to transmit. said carrier frequency pulses. y

23. A multi-channelY transmission system according to claim 21 wherein the separate identifying signal modulating means includes means for width shaping of the pulses of its respective chan-k nel to a width different from the pulse widths of other channels.

24. A multi-channel transmission system according to claim 21.wherein the separate identifyingsignal modulating means includes means for amplitude modulating the pulses of its respective channel to an amplitude different from the pulse amplitudes of other channels.

25. A multi-channel transmission system according to claim 21 wherein the separate identi* fying signal modulating means includes means for modulating the pulses of its respective channel with a signal of a frequency outside of the frequency band of the intelligence with which the pulses of such channel are modulated and which differs from the frequency of the identifying signal with which the pulses of other channels are modulated.

26. A multi-channel transmission system according to claim 21 further including means to intelligence Signals; fcbie 'mfiuimig characteristic of the pulses accordin'to oneinV telligence signal and meanrsvto modulate affsec- Gnd; Characteristic 0f the ...esacrdnsw' a se'oe'nq intelligence signal. "'f V '275A Asystem for selectively receiving a given channel of communicationfroin amulti-channel trainof pulses wherein the 'pulses of each channel differ from pulses oifother channels by predetermined identifying signal'modulation of some characteristic of the pulses and are further modu., lated according t0 tl'ieinstataneoussignal values of intelligence exclusive 'f'the identifying signal modulation, colijiprising;v means vfor segrega'tfing from the trainer channel pulses those pulse'stof a given identifying signal, and means for demodu; latine the segregated pulses toV obtain ligence with which they are modulated;

28. A system' according to claim 2,7 'wherein the characteristic of the pulses'modulated byk iden? tifyingA signals is amplitude, and'fthemeans for segrl'gating theY pulses of afgiven ehannelfirom said train of multi-channel pulses includesmeans to eliminate' those pulses of 'greater andlesser amplitude than the 'amplitudes of the pulses' ofi said givenchan'nel.

29.` A lsystem' accordingtoclaim 27 wherein theV characteristic of the pulse'sfnddulated'by identifrying'r signals is Width,v and the means for segregating the pulses `Vfiajgiven 'channel from-said train ofymulti-'c'hannel pulses'. includes means for passing pulseenergy 'of avvidtli according tothe identifying pulse vvi'dth ofesacli 'givenchan'nel veX- clusive of the identifyinglpuls'e "Widths of ether channels.

30.: A system according to clairn 27wherein the characteristic of the pulses,modulated-by'identifying signals is frequency signals exclus'ivd'f the'frequency bands 'oftl'1ei intelligenc"witli whinzlithey pulses or 'saidrchannels are modulated,

selector means'to passsuccessivelyffor 'shortinY-l' tervals 'per 'channel the pulses of said Vchannels, for demodulation, I'neans'fordemod ulating the pulses passed byv s'aid'slectorl means; Vand means responsive` to the `identifying signal frequency of" a given 'channel for'timingr saids'elect'or 'means' for passage' only of pulses" Y 31. A system according to claiin 27 wherein 'the h channel simultaneously carriesftwo e the mtei-v n disais given channel; 50

"i tive'reeption 0f Channels'. A ,t

a groupA by, a train. of. interi-. -v

` oif some characteristic thereof and in addition aretinodulated in someother characteristic, er;`

elusive of,y the mst-mentioned, characteristic ac.'- cordingtto the instantaneusignal values of in.- telligence to be conveyed; comprisingmeans to., receive said trainy of pulses, 'anda plurality of branch circuits coupled'in parallel to said means' demodulating means is capable of separating two' intelligence signals from denh1y''modulatedpulses,l

modulating pulse 'energy ofthe doubly'modulated iwhicli .they are modulated.

each branch circuit having means'for selectively. segregating from said train` t l siredvchannjel and mea-ns fordemodulatingftlie segregated pulses to olfitaintheY intelligence with;

EMILE LABIN. DONALD1 D.. GRIEG. 1i,EfirRn\ici:s CITED.

The following references are of recordin the file of thispatent:

UNITED STATES PafrnnfrsV those pulses of a 'def-' 

